. Kirkes' handbook of physiology . ULSE 161 the period which precedes the ventricular systole the quiet heart rests with itsapex against the wall of the chest. When the ventricles contract, their wallssuddenly become firm and tense. Being firmly attached at the base the effectof the movement is to press the hardened ventricle against the chest discharge of the contents of the ventricle into the curved aorta intensi-fies this pressure by its mechanical effect in tending to straighten the curveof that vessel and thus holds the ventricle in firm contact with the is this sudden p
. Kirkes' handbook of physiology . ULSE 161 the period which precedes the ventricular systole the quiet heart rests with itsapex against the wall of the chest. When the ventricles contract, their wallssuddenly become firm and tense. Being firmly attached at the base the effectof the movement is to press the hardened ventricle against the chest discharge of the contents of the ventricle into the curved aorta intensi-fies this pressure by its mechanical effect in tending to straighten the curveof that vessel and thus holds the ventricle in firm contact with the is this sudden pressure of the contracting heart against the chest wall thatis felt on the outside. The impact or shock is possibly more distinct becauseof the partial rotation of the whole heart toward the right and front alongits long axis. The movement of the chest wall produced by the ventricularcontraction against it may be registered by means of an instrument calledthe cardiograph; and the record or tracing, called a cardiogram, corresponds. Fig. 157.—Typical Cardiogram (upper trace) from the Dog. Taken simultaneously with theaortic pressure (middle) and intraventricular pressure (lower) tracings. Time in of a second.(Hiirthle.) almost exactly with a tracing obtained by an instrument applied over thecontracting ventricle itself. The cardiograph, figure 156, consists of a cup-shaped metal box overthe open front of which is stretched an elastic India-rubber membrane uponwhich is fixed a small knob of hard wood or ivory. This knob, however,may be attached, as in the figure, to the side of the box by means of a spring,and may be made to act upon a metal disc attached to the elastic membrane. The knob is for application to the chest wall over the place of the greatestimpulse of the heart. The box or tambour communicates by means of anair-tight tube with the interior of a second or recording tambour suppliedwith a long and light writing lever. The shock of the hearts impulse beingcommun
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